1. Field of Invention
This invention relates to laser systems and methods of operation. More particularly, the invention relates to a laser system and method of operation having improved signal continuity and safety.
2. Background Discussion
Laser systems have many applications in the commercial, medical and educational environments. Laser light differs from ordinary light in three ways: it is monochromatic, coherent and directional. One of the key issues with lasers is their safety of operation. A great deal of energy is focused on a small are which may be beneficial or destructive according to the environment. For example, laser systems employed by laser pointer in an educational presentation may cause accidental exposure of the laser beam by the audience. Thus, the laser frequency and power output are minimized to avoid tissue damage should accidental exposure to the beam occur.
Another key issue with this laser, is their continuity of operations in the event of a safety problem. For example, lasers are often used for short-range, line-of-sight communications such as between two buildings separated by a right of way that prevents buried cables. The communication lasers operate at a much higher power than educational pointers. However, even though the laser system is carefully aligned from a transmitter to a receiver and sealed from accidental exposure by maintenance personnel, the possibility still exists for the beam to be broken by maintenance personnel or birds flying through the area, etc. The inadvertent exposures xe2x80x9cbreaks xe2x80x9d the beam and cause loss of signal continuity, as well as potential personal damage to the object breaking the beam. As a result, laser safety and signal continuity are often addressed by mechanical shielding and interlocks around the emitter and receiver and reduced power which contributes to reduced signal range. In any case, the transmitted laser beam is not enclosed as a protective measure from accidental interruption of the beam.
Prior art related to laser beam safety and signal continuity includes the following:
WO/017691 A1, entitled xe2x80x9cCoupling Lens and Semiconductor Laser Modulexe2x80x9d, issued Mar. 30, 2000 and filed Sep. 10, 1999, discloses a coupling lens for coupling the emerging length in the emerging length beam from a semi-conductor laser to an optical fiber. The coupling lens comprises a single lens integral with a diffraction lens composed of concentric ring bands on the planes of incidents or plane of emergence of a single lens. The diffraction lens has a positive refractive power. The relief function of the diffraction lens is generally an isosceles triangle. When the coupling lens is used with a semiconductor module, the output power of the module can be so controlled as to conform with the safety standards even if the attenuation film, polarizer or optical fiber comes off without any control circuits or automatically stopping the lasing of the laser.
JP 1269188A2, entitled xe2x80x9cBar Code Scanning Devicexe2x80x9d, issued Oct. 26, 1989 and filed Dec. 20, 1988, discloses a laser beam scanning device having a window arranged mat side and upper part of the transfer path of an article being scanned. The surface of the window is arranged to be inclined obliquely upwards at an angle larger than 90xc2x0 to the transfer surface of the transfer path and plural scanning luminous fluxes with mutually different directions are directed to the scanning area on the transfer surface in front of the window. The laser-scanning device is oriented so as to not directly project the luminous flux to an operator performing a medical operation in front of the scanning area. That is, commonly, the head part and the breast part of the operator do not receive the scanning laser beam at all. Thus, an optimum workplace is obtained in the aspects of human engineering and also in safety.
JP 5218972 A2 entitled, xe2x80x9cFree Space Laser Communication Equipment and Methodxe2x80x9d, issued Aug. 27, 1993 and filed Jul. 30, 1992, discloses a terminal equipment which sends a laser beam at a level below a safety threshold. A microprocessor sends a terminal equipment identification code together with a beam. An Acknowledgment signal from the receiving terminal equipment is monitored and the window signal is received. The microprocessor activates the laser in a normal level of high power to enhance a communication performance. When the acknowledgment signal is monitored and the signal is not received for a prescribed time or, it is regarded that a disturbance or misalignment of the beam has taken place, the laser power is reduced to a level safe for transmission. Thus, the safety of an unconscious observer is assured and the communication performance is improved.
None of the prior art discloses a laser beam insulated from intervening objects and protected from signal loss due to objects blocking the light beam and in the event of such blocking performing recovery of the signal in an efficient manner.
An object of the invention is an improved laser system and method of operation having signal continuity and safety of operation from intervening objects.
Another object is an improved laser system and method of operation providing a central beam and a surrounding guard beam preventing signal interruption from intervening objects
Another object is an improved laser system and operation for restoring signal continuity without loss of information when the laser is interrupted by an intervening object.
Another object is a laser receiver having a dual lens system, one lens receiving a main laser beam and the other lens acting as parallel receivers for a surrounding guard beam.
Another object is a trigger circuit recognizing interruption of a laser guard beam surrounding a main laser beam and altering the performance of the main laser beam according to the nature of the interruption
Another object is an improved laser system and method of operation for medical application in confining the laser beam to a defined area.
These and other objects, features and advantages of the invention are achieved in a laser system comprising a main laser beam, typically provided by a high power Continuous Wave (CW) laser. The main laser beam is surrounded by a guard laser beam coaxially aligned with the main laser beam. The guard laser beam is typically provided by a low power, pulse beam laser. A receiver includes a single lens and a surrounding angular segmented set of mirrors and lens acting as parallel receivers. The main laser beam is received by the single lens and provided to a receiver. The guard laser beam is received by the annular, segmented set of mirrors and lens acting and provided to a trigger circuit. In operation, the guard beam insulates the main laser beam from interruption. If the guard beam is interrupted at any point along the length of the beam, one or more of the parallel receivers will be blocked and a signal will be provided to trigger circuit to alter the performance of the main laser beam, including shut down, via a return laser transmitter to the main laser. The main laser performance is altered according to the nature of the interruption. In the case of shut down of the main laser, the current stream of bits or packets is buffered and discharged when the main laser is turned on after the interruption is cleared. If the main laser is a pulsed beam laser, the shutdown may consist of simply not pulsing the laser at the next pulse time. The guard laser beam is never deactivated during shut-down of the main laser. Once the guard beam interruption is cleared, the trigger signal ends and the main laser is reactivated. To prevent cross talk between the CW and pulsed beam laser, different lasing materials and different frequencies are used. If the main and guard lasers are pulse lasers, then different pulse rates are used. The system may also include sensors for detecting climatic conditions affecting the guard beam. For example, a driving rainstorm or dust clouds, both of which disperse the guard band, but not alter the operation of the main laser. External sensors detect these conditions and activate the trigger circuit, which would maintain the continuity of the main laser in the presence of the climatic condition. Optionally, the laser return system may be activated by the trigger system to increase or reduce the power level of the main laser. Thus, the continuity, safety and signal restoration of a laser beam communication system are provided against intervening objects.